Crude oil occurs naturally in reservoir formation mostly as pressurized liquid, which is the main driving mechanism for hydrocarbon primary recovery where wells are drilled into underground reservoirs. Once the pressure is depleted, a significant portion of total amount of oil in the reservoir is left behind and thus only a fraction of the oil in the ground can be recovered. Secondary (waterflooding, natural gas reinjection, air injection, carbon dioxide injection) and even tertiary (surfactant, polymer flooding, thermal recovery and in-situ combustion) techniques are required to enhance the hydrocarbon recovery factor from reservoirs.
Waterflooding is probably one of the most common secondary recovery techniques. Aqueous fluids are injected at one or more points in the reservoir at a pressure sufficient to effect a displacement of the oil from the pores of the reservoir and to push the oil ahead of the water front to the production well or wells. This technique is adequate as long as the water is available in large quantities, cheap and maintains a high displacement efficiency. In general though waterflooding by itself has a poor displacement efficiency as a result of the high interfacial tension (IFT) between water and oil. IFT contributes to the capillary retention of the discontinuous oil phase and thereby prevents its displacement. Therefore, chemical additives such as surfactants, which are wetting agent s that lower the interfacial tension between fluids or substances, are added to the water flood to enhance oil recovery. Surfactant-based techniques are typically categorized as a tertiary recovery method to distinguish it from the usual waterflooding.
The use of chemical additives in aiding oil to move easily through the reservoir requires a fundamental understanding of the interaction chemistry of these additives with oil, salinity and rock heterogeneity. To examine such processes on a molecular level is beyond what the classical core flooding experiments can provide. An alternative approach that is used to minimize the costly and time consuming experimentation is molecular modeling, which provides detailed information about material at the molecular or atomistic level. Molecular modeling can be used to assess the effectiveness of chemical additives in oil recovery by understanding their fundamental role in the recovery of oil and then optimizing their use to improve it.
Molecular Dynamics modeling is already used in biology, pharmacology and catalyst research to gain a better understanding of the interactions taking place at molecular and sub-molecular levels and/or assess the efficiency of some molecules as medications.
Some of these known methods and further information relating to others modeling methods within and outside the field of hydrocarbon recovery can be found for example in the following references: